Speex (SPX) is an open source audio compression format designed for speech in voice applications. It is based on the CELP algorithm, one of the variants of which we have already discussed in the article about converting QCP files. Compared to other voice codecs, Speex has made a big step forward and provides higher quality.
1 Speex in a few words
Speex was the best ubiquitous format for compressing human speech, but was eventually replaced by the more versatile Opus codec. Contrary to expectations, Opus uses the SILK codec for speech compression, and the CELP implementation for full-band signals. Speex developments did not find a place in the new format. The legacy of Speex now lies in the DSP library for acoustic echo suppression and automatic level control.
I mostly saw Speex files in Asterisk and LinPhone IP telephony apps, where it did a great job of replacing the old GSM. I would have long forgotten about it if I hadn't encountered some video files that lacked audio. As it turned out, the unknown audio codec for Windows was Speex. Frankly speaking, its use in MP4 files was an unpleasant surprise.
Considering the above, the format is still alive and there is a need to simultaneously convert several Speex files to a more compatible format while maintaining good spoken audio quality.
2 Best Way to Convert SPX to MP3
Audio Converter Plus is the best and user-friendly audio converter software that can help you convert your recordings while maintaining speech intelligibility. So you can listen to your voice messages on MacOS, Windows, and Linux platforms. Now, we'll walk through this in four simple steps.
Step 1. Free Download and Install the Program
Here you can free download the Audio Converter Plus software and install it on your computer, then you can launch the program to open the main interface.
Step 2. Add SPX Audio FileAfter opening the main interface of this SPX to MP3 converter tool, you can click the "Add Files" button to load SPX audio files into the program one by one. Or you can simply drag and drop one or more .spx files into this software.
By the way, if the voice recording contains background noise or music, then you can isolate it using VocalRip AI.
Step 3. Select Output SettingsThen you can click the "Output Format" drop-down arrow to open the list and select "MP3" as the output format.
Click the "Codec Options" button to open the window to select the audio compression parameters such as Bitrate, Sample Rate and Channels as you like. Finally, the audio quality will be optimized according to your settings.
Step 4. Convert Speex to MP3After setting up all the audio files, you can click the "Convert" button. The most important advantage over online converters is the ability to process thousands of files at a time, while normalizing the volume to the same level.
3 Convert Speex to MP3 online
Convertio is one of many freemium online SPX to MP3 converters. It allows you to convert Speex files from both your local computer and online sources. If you have a lot of files to convert, you won't be able to do it for free. The limit is 25 files per day and no more than 2 files at a time.
Step 1. Open the Convertio website and go to the Audio Converter section.
Step 2. Drag and drop audio files to the specified area from your computer, Google Drive or Dropbox. Wait for the files to upload to the site.
Step 3. Start converting and your files will be added to the general queue. If the service is heavily loaded, you will have to be patient. The best option is to switch to solving other tasks and return to the page with files later. Converted files are stored in the service for 24 hours.
4 Conclusion
Batch conversion of Speex files was no more difficult than with other formats. But it had an unexpected surprise for us - the resulting files grew significantly in size. Speex, as a voice codec, contains a voice activity detector and uses a variable compression ratio, which is not available in classic audio codecs such as MP3.